A condensed cycloaliphatic compound, decahydronaphthalene, and cross-linking cycloaliphatic compounds, norbornane, tricyclodecane, tetracyclododecane, bicyclo[2.2.2]octane and adamantane, are excellent in low specific gravity, hydrophobicity, transparency, heat resistance, and environmental stability. Moreover, it is known that (meth)acrylate, which has the above condensed cycloaliphatic compound or cross-linking cycloaliphatic compound in its intramolecular structure, also has the aforementioned excellent properties. A method of synthesizing such (meth)acrylate is described, for example, in Japanese Patent Publication No. 5-27643, Japanese Patent Publication No. 7-13038, Japanese Patent Laid-open No. 63-8355, and Jpn. J. Appl. Phys., 35, 528 (1996).
A cyclic ester, γ-butyrolactone, is transparent, highly polar and soluble in water, as well as being a good solvent for various types of organic low molecular weight compounds and polymers. Additionally, as opposed to β-propione ring, δ-valerolactone ring and ε-caprolactone ring, γ-butyrolactone ring itself has almost no polymerizing ability, and therefore it is extremely chemically stable and is also excellent in heat stability. For these reasons, it is expected that (meth)acrylate having a γ-butyrolactone ring in its molecule is also excellent in transparency, high polarity, solubility and stability. A method of synthesizing such (meth)acrylate is described, for example, in Japanese Patent Laid-open No. 10-212283 and Japanese Patent Laid-open No. 11-269160.
In recent years, in some cases, a (meth)acrylate polymer used for component resins of a coating material, adhesive, agglutinant, resin for ink, resist or the like, is required to have hydrophobicity, heat resistance, moderate polarity, and solubility in various organic solvents, as well as transparency and stability.
To realize these properties, there has been proposed a method of copolymerizing (meth)acrylate comprising a condensed ring structure or a cross-linking ring structure in its molecule with (meth)acrylic acid (or (meth)acrylate) having a hydrophilic functional group. For example, J. Photopolymer Science and Technology, 7[1], 31 (1994) describes a method of copolymerizing 1-adamantyl methacrylate, t-butyl methacrylate and methacrylic acid. Proc. of SPIE, 2438, 433 (1995) describes a method of copolymerizing tricyclodecanyl acrylate, tetrahydropyranyl methacrylate and methacrylic acid. J. of Photopolymer Science and Technology, 8[4], 623 (1995) describes a method of copolymerizing isobornyl methacrylate, methyl methacrylate, t-butyl methacrylate and methacrylic acid. However, in some cases, polymers obtained by these methods have too strong hydrophobicity, or they are inferior in stability.
It can be expected that (meth)acrylate which has both a condensed ring structure or a cross-linking ring structure such as decahydronaphthalene, norbornane, tricyclodecane, tetracyclododecane, bicyclo[2.2.2]octane and adamantane, and a γ-butyrolactone structure in a molecule, has high polarity and solubility in various solvents deriving from the γ-butyrolactone structure, as well as hydrophobicity and heat resistance deriving from the condensed ring structure or the cross-linking ring structure. And the above effects can be expected even from a condensed ring structure or a cross-linking ring structure combining a simple cycloaliphatic structure such as cyclopentane and cyclohexane with the γ-butyrolactone structure.
Accordingly, Japanese Patent Laid-open No. 2000-26446 proposes a copolymer obtained by copolymerizing 5-(meth)acryloyloxy-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic-6-lactone. However, 5-(meth)acryloyloxy-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic-6-lactone is a solid at an ordinary temperature and it is not always sufficiently soluble in organic solvents, so that it is not easy to produce the (co)polymer by solution polymerization.
By the way, in recent years, a microfabrication technique has quickly progressed against the backdrop of the development of a lithography technique so as to realize high-density and high-integrated devices, in the field of microfabrication technology for production of semiconductor devices or liquid crystal devices. As such a microfabrication technique, an exposure radiation source having a shorter wavelength has generally been used. Specifically, the exposure radiation source has been changed from the conventional ultraviolet ray, such as a g-line (wavelength: 438 nm) and i-line (wavelength: 365 nm), to far ultraviolet ray.
Presently, a KrF excimer laser (wavelength: 248 nm) lithography technology has been introduced in the market, and an ArF excimer laser (wavelength: 193 nm) lithography technology, which is directed towards the conversion of an exposure radiation source into the source with a further shorter wavelength, is being introduced. Moreover, an F2 excimer laser (wavelength: 157 nm) lithography technology is studied as the next generation technology. Furthermore, an electron beam lithography technology, which somewhat differs from the above technologies, is also intensively studied.
As a resist with high sensitivity to such a light source with a short wavelength or electron beam, a “chemically amplified resist” has been proposed by International Business Machine (IBM) Corporation, and at present, the improvement and development of this chemically amplified resist have vigorously been progressing.
By the way, a resin used for the resist is also forced to change its structure in the conversion of the light source into the one with a shorter wavelength. For example, in the KrF excimer laser lithography, polyhydroxystyrene having high transparency to the light with a wavelength of 248 nm, a hydroxy group thereof protected with an acid-dissociating solubility-inhibiting group or the like is used. However, in the ArF excimer laser lithography, the above resin cannot always be used because its transparency is insufficient to the light with a wavelength of 193 nm.
Accordingly, as a resist resin used in the ArF excimer laser lithography, an acryl resin or cycloolefin resin that is transparent to a light with a wavelength of 193 nm becomes the focus of attention. Such an acryl resin is disclosed in publications such as Japanese Patent Laid-open No. 4-39665, Japanese Patent Laid-open No. 10-207069 and Japanese Patent Laid-open No. 9-090637, and such a cycloolefin resin is disclosed in publications such as Japanese Patent Laid-open No. 10-153864 and Japanese Patent Laid-open No. 10-207070. However, these resins are still insufficient in their performance, and further higher dry etching resistance is required.
As means providing both transparency to the light with a wavelength of 193 nm and high dry etching resistance, Japanese Patent Laid-open No. 2000-26446 discloses a method of copolymerizing 5-(meth)acryloyloxy-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic-6-lactone or the like as a monomer unit.
The thus obtained copolymer offers excellent performance as a resist resin. However, 5-(meth)acryloyloxy-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic-6-lactone is a solid at an ordinary temperature and is inferior in solubility in organic solvents. Accordingly, it is extremely difficult to eliminate unreacted monomers remaining in a polymerization solution in the process of reprecipitating a resist resin synthesized by solution polymerization, and sometimes it may affect resist some kinds of performance such as transmittance. Moreover, in general, a resist resin obtained by copolymerizing 5-(meth)acryloyloxy-6-hydroxybicyclo[2.2.1]heptane-2-carboxylic-6-lactone is also inferior in solubility in organic solvents, and therefore conditions for obtaining a resist resin by solution polymerization are strictly limited.